One of the most significant problems facing the transportation industry over the years has been thefts from railroad cars, trailer trucks, transport containers and the like. These thefts often occur in railroad freight yards where the cars, trucks and containers may be located while awaiting further transport.
Such thefts are often made by non-professional thieves such as juveniles, who will break the seal on a car, truck or container when it may be located in a remote corner of the yard.
It was often the case that such thefts were not detected early enough to recover the material removed. In such circumstances, the fact that the seal on the car, truck or container was broken made the entire contents subject to rejection at the destination.
The use of padlocks was found to be impractical because of the problem of transfer of keys, their susceptibility to being defeated by crowbars and other means for overcoming them which are readily accessibly to thieves, both professional and amateur.
As a result of these problems various devices were proposed for attachment to the latch of a railroad car, truck or container to prevent such pilferage. One such device is disclosed in U.S. Pat. No. 3,980,337, which issued on Sept. 14, 1976 for LOCKING SEAL and which is assigned to the same assignee of the present invention. That patent discloses a locking structure where in a male member is receivable within a locking body and retained by a snap ring which cooperates with annular channels in the male member and locking body to lock the elements together. Attempts to withdraw the male member from the locking body caused the snap ring to be forced more tightly into locking position thereby frustrating defeat of the lock.
The lock structure disclosed in U.S. Pat. No. 3,980,337 has also been found to be suitable for locking devices where an extended bolt is used to be passed through the staple of a latch such as those found on trucks, railroad cars and containers to effect locking. In this regard both the cable type locking seal and the rod or extended bolt type locking seal have been well received in the industry and commercially successful. In fact, until recently, there has been no known way to defeat the purpose of such seals, particularly by non-professional thieves. The only known way to remove the locking seals has been to use a large bolt cutter to cut the cable or extended bolt thereby destroying the lock and precluding its being used after opening.
The ingenuity of dishonest persons, however, is boundless. After years of successful secure use, it has now been found that locks such as that shown in U.S. Pat. No. 3,980,337 used with a rod rather than a cable can be defeated. More specifically, it has been found that by establishing a relatively high speed rotation between the lock body and the bolt, and thereafter exerting force to disassemble the bolt from the lock body, the locking spring is rendered ineffective and the bolt can be withdrawn. The rotation between the lock body and the bolt can be established by securing the lock body within the chuck of a large electric drill and rotating the body while holding the bolt against rotation and exerting a force to withdraw the bolt.
It is not altogether clear how the relative rotation between the two members permits their disassembly. One theory is that the rotation of the lock body results in the harder steel of the spring acting as a cutting tool to remove a portion of the groove on the bolt thereby permitting the spring to be displaced out of the groove and the bolt to be withdrawn. Another theory is that the rotation of the lock body in cooperation with forces exerted on the spring by the attempted displacement of the bolt, cause the spring to rotate out of the channel in the bolt thereby permitting removal of the bolt. Whatever the phenomenon that occurs under these conditions, the net result is that the bolt can be removed and the lock defeated.
Upon learning of the problem, applicants attempted many approaches to its solution. One approach was to vary the angle of incline of the recessed surface in the lock body from the design angle of thirty degrees (30.degree.) so as to alter the force sectors acting in the locking spring. This was to no avail. Another approach was to change the depth and configuration of the channels in the bolt and lock body. These proposals also failed. Thus, applicants were faced with the problem of how to structure a locking device of the general type in question such that it would not be defeated by establishing relative rotation between the lock body and the bolt and, while rotation continues, removing the bolt.